1. Field of the Invention
This invention relates to grinding and comminuting apparatus in general, and in particular to an industrial hammer mill having a reciprocating feed, reversible operation, and special shear plates in the grinding stator to increase comminuting efficiency while reducing jamming of and damage to the mill by refuse that cannot be comminuted.
2. Brief Description of the Prior Art
Grinding mills have been utilized for some time in a variety of applications. For example, grinding mills have been commonly used in the past for grinding grains, corn, hay, and other forage materials for livestock feed, as well as paper for cellulose insulation and other commercial uses. Many varieties of grinding mills for comminuting such materials have been developed, such as stone mills, burr mills, hammer mills, and roller mills. Because forage materials tend to be fibrous and stalky, hammer mill type grinders have been found to be the most effective in comminuting these forage or roughage materials. However, handling and feeding these bulky, fibrous, stalky materials into a hammer mill in a uniform manner proved to be quite difficult and required a good deal of tedious manual labor, because they do not flow in a uniform manner like grains grains.
Some of the more recent developments in larger grinding apparatus to alleviate the problems in feeding bulky, fibrous, and stalky materials into hammer mills include the grinders now known generically as tub grinders because of their rotating tub feeders. Typical examples of such tub grinders can be found in the following patents: U.S. Pat. No. 2,659,745, issued to W. Wortman; U.S. Pat. No. 3,615,059, issued to E. Moeller; U.S. Pat. No. 3,743,191, issued to R. Anderson; U S. Pat. No. 3,912,175, issued to R. Anderson; U.S. Pat. No. 3,966,128, issued to J. Anderson, et al.; U.S. Pat. No. 4,003,502, issued to E. Barcell; U.S. Pat. No. 4,087,051, issued to C Moeller; and U.S. Pat. No. 4,106,706, issued to H. Burrows. These tub grinders were designed initially to feed very large bales of hay and other forage materials into hammer mill apparatus without the need for excessive manual labor. Tub grinders come in various sizes depending on the type of duty for which they are designed, but all have relatively large rotating tubs positioned over the hammer mill cylinders for containing bales or piles of forage material and feeding the forage material gradually into the hammer mills. In a typical tub grinder, the hammer mill cylinder is positioned under and extends partially through the floor or bottom of the tub, and the rotating tub feeds the bottom of the bale or pile of material to be comminuted over the hammer mill. The hammers on the hammer mill cylinder rotate at a high angular velocity and "chew" off the forage on the bottom of the bale as the base of the bale rotates over the hammer mill cylinder in the floor of the tub.
Such tub grinders are quite effective for grinding large quantities of forage or roughage materials. Therefore, with the exception of expensive, large, stationary grinders in more or less permanent industrial grinding installations with special, custom designed conveyors and other feed apparatus for specific purposes, the tub grinders have become the standard for larger, portable, mid-priced, general purpose grinding machines. Consequently, tub grinders are also now being used with marginal success for comminuting other kinds of bulky materials where large quantities of such materials have to be handled, and particularly where the materials are dumped into the hammer mill in batches, such as with a front end loader vehicle. For example, some tub grinders are being used to comminute waste materials, such as wood and other construction industry wastes, tree branches and landscaping waste, refuse, rubbish, and the like, and a few heavier duty models are being made especially for those uses.
Unfortunately, however, even the largest tub grinders or millers are not really well-suited to the task of such heavy waste or industrial grinding. The rotating tub concept, which worked so well for grinding hay bales that it revolutionized large scale, portable batch feed grinding, does not work as well with waste wood, cement chunks, metal, and other materials from construction sites, tree branches and grass and weed cuttings from landscape maintenance operations, refuse, rubbish, volcanic rock, and the like.
In the past, there was not a great need for grinding mills that could reliably grind such tough or odd-shaped materials, since most of these materials were simply hauled to the nearest landfill site for disposal. Nowadays, however, the decreasing availability of landfills for rubbage or refuse disposal has placed a greater emphasis on the need to transform such materials into more compactable and readily decayable forms before disposal. Consequently, most local and municipal governments are beginning to require city workers to grind waste materials, such as large tree branches, wood, assorted rubbish, and other waste collected from parkways, parks, schools, etc., into more readily decayable forms before hauling them to the landfills, thereby easing the refuse disposal problem. Moreover, this idea of grinding rubbish or refuse into a more disposable and quickly decayable form is spreading into other areas, such as garbage collection companies, which have to dispose of large amounts of these materials. Therefore, there is a steadily increasing need for an industrial grinder or miller that is capable of grinding large quantities of such difficult or heavy materials more reliably and efficiently. Such an industrial grinder should be capable of reliably grinding all types of shreddable materials such as garbage, refuse, waste, glass, plastics, paper, clay, wood, branches, yard waste, manure, bark, wet leaves, grass clippings, weeds, compost, and other common, but shreddable waste materials, yet not jam when certain non-comminutable material, such as chunks of metal, rock, or concrete might accidently find its way into the mill.
Further, because of the very common use of front end loader vehicles to handle and move such waste materials, the industrial grinder should be capable of receiving fairly large batch quantities of such materials and feeding them uniformly and efficiently into the hammer mill rotor for comminuting. It should also be capable of handling not only bulky, irregular-shaped objects, but also capable of taking occasional chunks of non-comminutable material, such as metal, rock, concrete, and other hard objects without damaging or jamming the hammer mill rotor or concave apparatus. Prior to this invention, no such industrial grinder existed